Deletion of POMT2 in Zebrafish Causes Degeneration of Photoreceptors

Int J Mol Sci. 2022 Nov 26;23(23):14809. doi: 10.3390/ijms232314809.

Abstract

Mutations in the extracellular matrix protein eyes shut homolog (EYS) are a common cause of retinitis pigmentosa, a blinding disease characterized by photoreceptor degeneration. EYS binds to matriglycan, a carbohydrate modification on O-mannosyl glycan substitutions of the cell-surface glycoprotein α-dystroglycan. Patients with mutations in enzymes required for the biosynthesis of matriglycan exhibit syndromic retinal atrophy, along with brain malformations and congenital muscular dystrophy. Protein O-mannosyltransferase 2 (POMT2) is an enzyme required for the synthesis of O-mannosyl glycans. To evaluate the roles of O-mannosyl glycans in photoreceptor health, we generated protein O-mannosyltransferase 2 (pomt2) mutant zebrafish by CRISPR. pomt2 mutation resulted in a loss of matriglycan and abolished binding of EYS protein to α-dystroglycan. Mutant zebrafish presented with hydrocephalus and hypoplasia of the cerebellum, as well as muscular dystrophy. EYS protein was enriched near photoreceptor connecting cilia in the wild-type, but its presence and proper localization was significantly reduced in mutant animals. The mutant retina exhibited mis-localization of opsins and increased apoptosis in both rod and cone photoreceptors. Immunofluorescence intensity of G protein subunit alpha transducin 2 (GNAT2) antibody (a general cone marker) and 1D4 antibody (a long double cone marker) in mutant retinas did not differ from wild-type retinas at 1-month post fertilization, but was reduced at 6 months post fertilization, indicating significant cone degeneration. These data suggest that POMT2-mediated O-mannosyl glycosylation is required for EYS protein localization to the connecting cilium region and photoreceptor survival.

Keywords: congenital muscular dystrophy; inherited retinal degeneration; photoreceptor degeneration; retina; retinitis pigmentosa; zebrafish.

MeSH terms

  • Animals
  • Dystroglycans / genetics
  • Dystroglycans / metabolism
  • Muscular Dystrophies* / metabolism
  • Retinal Cone Photoreceptor Cells / metabolism
  • Retinal Degeneration* / genetics
  • Retinal Degeneration* / metabolism
  • Retinitis Pigmentosa* / genetics
  • Zebrafish / genetics
  • Zebrafish / metabolism

Substances

  • Dystroglycans